Last month, human cases of West Nile Virus in the United States increased sixteen fold in three weeks, soaring to 715 cases by August 21 from 44 cases at the end of July. According to the federal Centers for Disease Control, the explosion coincides with the onset of West Nile Virus season, which lasted six weeks in 2002. By the end of last year, 4,156 human cases (including 284 that were fatal) had been reported in 44 states.
Hawai’i has so far escaped the virus. But every day, with the arrival of tourists and ongoing traffic in birds, the state is exposed to potential pathways for the introduction of the virus. If it becomes established in Hawai’i, not only could it wreak havoc on the tourism-based economy, it could also devastate native Hawaiian birds. According to David Duffy, biologist at the University of Hawai’i at Manoa, the threat of West Nile Virus coming to Hawai’i is “very, very real.”
To minimize that threat, a broad coalition of agencies – state, federal, public, and private – has organized itself as the WNV Prevention Group. Members include the state Departments of Agriculture, Land and Natural Resources, and Health; the federal Department of Agriculture, and the Department of Interior’s Fish and Wildlife Service and U.S. Geological Survey Biological Resources Division; the U.S. Postal Service; the University of Hawai’i; and private groups including the Hawaiian Humane Society, the Honolulu Zoo, Ducks Unlimited, and the Nature Conservancy of Hawai’i.
Heading up the group is Jeff Burgett of the Fish and Wildlife Service. “Hawai’i is relatively isolated and depending on our luck, we may be able to keep it out indefinitely,” he told Environment Hawai’i. Burgett’s interest in the virus stems from his efforts to restore populations of the ‘alala, or Hawaiian crow. West Nile Virus has hit crows particularly hard on the U.S. mainland, although they are still abundant. Should the disease hit the ‘alala, however, whose total population numbers just 41, it would almost certainly ruin any chance for recovery of the species.
Peter Daszak, executive director of the Consortium for Conservation Medicine, began working this summer with the WNV Prevention Group. His consortium, based in Palisades, New York, was formed to study the effects of disease on global economies and ecologies; members include Harvard Medical School’s Center for Health and the Global Environment; Tufts University School of Veterinary Medicine, and the U.S.G.S. National Wildlife Health Center. For Daszak, the West Nile Virus is part of a larger international picture of emerging infections diseases that he calls “pathogen pollution, a form of human environmental change, like chemical pollution.” International trade gives pathogens free rides around the globe, where they can thrive in new and supportive hosts. At least two species have been documented to become extinct from diseases introduced through human activity, Daszak has found.
There is an “increasing conflict between trade and conservation,” Daszak told Environment Hawai`i, adding that the challenge is to find ways to “allow trade but stop disease.” In his view, Hawai’i’s WNV Prevention Group is “leading the U.S. and the world in dealing with a disease before it enters the state.”
Actually, Hawai’i has already seen one case of West Nile Virus. Last summer, a tourist from Minnesota tested positive for WNV while vacationing in Hawai’i, according to Shokufeh Ramirez, epidemiologist for the state Department of Health. Apart from the impact on the infected individual’s health, such imported cases pose little threat, Ramirez says. Human infections produce small quantities of virus. “Best evidence shows that [infected] humans cannot infect mosquitoes,” she says, while human-to-human transmission of the virus is unknown.
In West Nile’s disease cycle, two infections – one in mosquitoes, another in birds – are necessary to propagate the virus. Hawai’i is already home to Culex quinquefasciatus and Aedes albopictus (the tiger mosquito), both of which are known to spread WNV in the continental United States. If the mosquito ingests blood infected with enough virus, WNV will pass through its gut and infect its body. The mosquito host is not made ill by the infection and will carry it for the rest of its life. The other half of the infection cycle occurs in birds. When an infected mosquito feeds on a bird, it leaves the virus in the bird’s bloodstream.
Given enough virus, the bird will become infected and may carry enough virus to infect the next mosquito seeking a meal.
Although it is widely thought that Hawai’i birds will be susceptible to West Nile Virus, a study is in the works to test that hypothesis. Carter Atkinson and Dennis LaPointe of the Kilauea Field Station of the U.S.G.S. Biological Resources Division are collaborating with Chris Brand of the USGS BRD to determine if the virus will infect ‘amakihi, a member of the Hawaiian honeycreeper family. Atkinson said the group plans to capture 30 high-elevation, malaria-free ‘amakihi over the next few months. The captured birds will then be sent to the National Wildlife Research Center in Madison, Wisconsin, where they will be infected with the virus.
“The ‘amakihi is a tough little bugger,” says Burgett. “If it can’t survive West Nile, other native birds would be in deep trouble. We’re talking potential extinctions.”
In the meantime, scientists are on the lookout for any infected birds in the islands. Last November, the Department of Health began testing dead birds for the virus.
Duffy, however, thinks the state should be doing more. “The state is monitoring dead birds – which is nice, but that will only tell us that the disease is here and established, i.e. it’s too late.”
At present, infected birds have two ways of entering the state: by plane or on the wing. Last year, excluding hatching eggs and day-old chicks, around 3,500 birds entered the islands. Only in September 2002 did the state Department of Agriculture block the import of birds through the mail, a system that bypassed inspection.
Since last year, too, the state Department of Agriculture has imposed a ban on the import of all birds not certified free of the West Nile Virus. The ban also requires all imported birds to enter the state at the Honolulu International Airport, where they are inspected and their certification is verified. If the birds are not certified, the state gives the importer 24 hours to ship the birds out. If that doesn’t occur, the uncertified birds are euthanized.
It is not so easy to control the arrival of birds that come on their own power. However, many scientists believe this is an unlikely route of infection. Some birds, such as the Pacific golden plover, spend their summers in the high Arctic regions of Alaska, northern Canada and Siberia and then migrate to overwinter in Hawai’i. So far, Arctic regions have remained free of WNV infected mosquitoes. Other birds, such as ducks, migrate from the west coast of North America, which is also free of the virus. (As of August, West Nile Virus had migrated as far west as the Rocky Mountain states, from New Mexico in the South to Montana in the North.)
Should the virus become established in the Arctic or the west coast, the chance that a sick bird could migrate to Hawai’i strikes most experts as remote. Still, according to Janice S. Okubo, communications director for the Department of Health, “the possibility cannot be entirely ruled out.”
Many of those studying the problem say that that the arrival of mosquitoes carrying the disease is the most likely way that West Nile Virus will make it to Hawai’i. “By banning import of birds older than hatching day, the state made a major step toward preventing the arrival of the virus,” says Duffy, the UH biologist. “However, an infected mosquito could easily hop on a plane or make the passage in a container” aboard one of the many cargo vessels bringing goods to Hawai’i.
Currently, prevention focuses on reducing the likelihood that mosquitoes will spread past points of entry. The Department of Health’s Vector Control Branch has established programs at airports and harbors where light traps monitor mosquito numbers and workers take steps to eliminate standing water where the insects might breed.
While fumigating incoming aircraft and ships might seem another effective way to reduce the chance that infected mosquitoes might find their way to Hawai’i, the Environmental Protection Agency banned pesticide spraying of commercial and military aircraft in 1979.
Will the West Nile Virus become established in Hawai’i? “It’s all a probability game,” says Burgett. “Are we 100 percent safe? No. But are we better off now? Yes.”
Duffy is a little less sanguine. “We are whistling past the graveyard,” he says. “The dead bird [testing] is a good try, but…”
— Trevor Stokes
Volume 14, Number 3 September 2003
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